Question

I have something like this in scala:

abstract class Point[Type](n: String){
    val name = n
    var value: Type = _
}

So far so good. The problem comes in a class that extends Point.

case class Input[Type](n:String) extends Point(n){
    def setValue(va: Type) = value = va
}

On the setValue line I have this problem:

[error]  type mismatch;
[error]  found   : va.type (with underlying type Type)
[error]  required: Nothing
[error]   def setValue(va: Type) = value = va

I have tried to initialize with null and null.asInstanceOf[Type] but the result is the same.

How can I initialize value so it can be used in setValue?

Answer 1

You should specify that Input implements Point with the generic type Type because for now, as it is not specified, it is considered as Nothing (I guess the compiler can’t infer it from the setValue method). So you have to do the following:

case class Input[Type](n:String) extends Point[Type](n){
  def setValue(va: Type) = value = va
}

More information

I answered this question for the compilation error (it does compile on scala 2.9.0.1). Moreover I saw this case class as the implementation for an existing type, like ‘Int’. The usage of _ is of course a bad idea in the abstract class, however it is not prohibited, but the _ is not always a null, it is the default value, for exemple: var x:Int = _ will assign the value 0 to x.